Republican lawmakers and aides worry that Mr. Trump has misunderstood Democrats’ incentives to stand firm and that he has deputized the wrong aides to press his case. And they question who — if anyone other than the president — has the authority to resolve the impasse. They describe a dysfunctional dynamic where even senior leaders in Mr. Trump’s own party never know quite what to expect from the president…

It happened again on Thursday. A group of Republican senators were trying to forge a deal to pair wall funding with legal status for undocumented immigrants brought to the United States as children, often known as Dreamers. Then Mr. Pence told them that their effort would not earn Mr. Trump’s support, effectively torpedoing the talks. Members of the group said they recognized that their proposal would rise and fall according to the whims of the president…

But hours later, the president contradicted Mr. Pence, saying in McAllen, Tex., that he would be open to a “broader” immigration deal that would “simultaneously” deal with the Dreamers and a wall — if senators would bring him one they could agree on.